The USA and places around the Caribbean Sea should be ready for the rest of the hurricane season to bring an above-average number of storms, two groups of forecasters said Thursday.

Hurricane Claudette coming ashore on July 15. It was the last storm to hit the USA.

NOAA

William Gray and his Colorado State University group are predicting 14 named storms in the this season — we've already had four — but expect August and September to be relatively calm, with storms peaking in October.

National Oceanic and Atmospheric Administration (NOAA) forecasters say a total of 12 to 15 tropical storms should form over the Atlantic Ocean, Caribbean Sea or Gulf of Mexico by the Nov. 30 end of the hurricane season. (Related: The hurricane season so far).

Gray's team expects eight of the 14 storms that generate the 39 mph winds needed to become a named tropical storms will become hurricanes, with winds of at least 74 mph. Three of these show grow into major hurricanes with winds of 111 mph or faster, the group says.

The NOAA forecasters see their expected 12 to 15 storms including 6 to 9 hurricanes with 2 to 4 becoming major hurricanes.

The long-term, seasonal average is 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes per year, but this average represents wide swings in numbers of storms from year to year.

Both teams use global climate factor that scientists, beginning with Gray in the 1970s, have discovered influence how many storms form. Neither group attempts to say exactly where and when storms will form and hit.

Two of the key factors they use include the global weather patterns known as El Niño and La Niña.

El Niño, which is characterized by warmer than normal water in the eastern Pacific Ocean, tends to stifle hurricanes, while La Niña, characterized by colder than normal eastern Pacific water, tends to encourage them. (Related: El Niño and La Niña).

Earlier this year a La Niña seemed to be forming, but that isn't happening.

"One might assume the Atlantic hurricane season would be less active than predicted in May since (La Niña) has not developed, but this is not the case," says Jim Laver, director of NOAA's Climate Prediction Center.

"In this instance, La Niña is not everything. It is possible to have an above-normal hurricane season without La Niña, just as long as the right atmospheric conditions such as wind and air pressure patterns are in place, as they are now."

These other factors include the fact that we're in a multi-decadal period with large numbers of hurricanes.

This period, which began in the early 1990s, is likely to last for at least another decade, says Stanley Goldenberg of NOAA's Hurricane Research Division.

In fact, Goldenberg says, this climatic swing has already helped to make 1995-2002 the most active period since 1944.

While neither group attempts to forecast where and when storms will form and hit, Gray's forecast says: "The probability of U.S. major hurricane landfall for the rest of the season is estimated to be about 12% above the long-period average."

And, Gary Bell, head of NOAA's team, says: "Many of the hurricanes this season will develop over the tropical Atlantic and move westward as they strengthen. These hurricanes could pose a threat to the United States and/or the Caribbean Islands."